1. Field of the Invention
The present invention relates to an image heating apparatus and a heater preferably used for a heating-fixing apparatus of an image forming apparatus such as a copying machine or a printer using an electrophotographic system or electrostatic recording system.
2. Related Background Art
Conventionally, in the case of an image forming apparatus using an electrophotographic system, the so-called heating-roller-type heating-fixing apparatus is widely used which heats and fixes a recording material carrying an unfixed toner image by passing the material through a nip portion formed by a fixing roller and pressure roller which are pressure-contacted with each other and rotated.
A halogen lamp set in the hollow metal core of a fixing roller is generally used as the heat source of a heating-roller-type heating-fixing apparatus in which the toner on the recording material is melted by using the heat transmitted from the inside of the core. It is necessary that the hollow core of the fixing roller has a wall thickness of 0.5 to 4.0 mm in order to have a sufficient mechanical strength and has a large heat capacity. Therefore, it is necessary to supply power to the halogen lamp even under a standby state and preheat the fixing roller.
Moreover, an on-demand film-heating-type heating-fixing apparatus is recently practically used to which power is not supplied for heating-fixing apparatus under a standby state to minimize the power consumption.
A film-heating-type heating apparatus is disclosed in the official gazettes of Japanese Patent Application Laid-Open No. 63-313182, Japanese Patent Application Laid-Open No. 2-157878, Japanese Patent Application Laid-Open No. 4-44075, and Japanese Patent Application Laid-Open No. 4-204980. A flat ceramic heater is generally used as the heat source of a film-heating-type. Heating and fixing are performed by setting a heat-resistant resin film (fixing film) between the ceramic heater and a pressure roller to form a pressure-contact nip and passing a recording material carrying an unfixed toner image between the fixing film and the pressure roller.
The above flat ceramic heater is disclosed in the official gazette of Japanese Patent Application Laid-Open No. 6-5356. The heater is obtained by forming a current-carrying exothermic resistance layer on one side of a flat slender high-insulating substrate made of alumina or aluminum nitride and the current-carrying exothermic resistance layer is protected by a glass film. A fixing film is used so as to slide with the protective glass film or so that the fixing film slides with a glass film by forming the glass film on the other side of the ceramic substrate. Therefore, the heat of the current-carrying exothermic resistance layer is transmitted to the fixing film through the glass film.
Various image forming apparatuses of printers and copying machines using the above film-heating-type heating-fixing apparatus have many advantages compared to a system for performing heating and fixing by using a conventional heating roller such as disuse of preheating under a standby state and decrease of wait time (on-demand fixing).
However, the conventional heating heater used to the above-described film-heating-type heating-fixing apparatus has the following problems.
That is, in the case of a heating-fixing apparatus, it is necessary to fix unfixed toner on a recording material in accordance with instantaneous heating than ever because operating speeds of copying machines and printers have been recently increased. However, the heat conduction of a heat-resistant resin film used as a fixing film for a conventional film-heating system does not have a heat conductivity enough to apply to high-speed printing.
Although it can be considered to raise the set temperature of a heater, it is not effective means because the set temperature of the heater is limited when considering heat-resistant temperatures of a resin used for a stay holder for holding a heater and other peripheral members.
To solve the above problems, it is possible to efficiently achieve heat conduction to a recording material by using a thin-wall metal sleeve having a high heat conductivity instead of a heat resistant resin as the base material of a fixing film as disclosed in the official gazette of Japanese Patent Application Laid-Open No. 10-319753. However, when using a conventional ceramic heater, a glass layer on the top surface of the heater scrapes against the inside of the metal sleeve. Even if a glass layer is not formed, the ceramic top surface scrapes against the inside of the metal sleeve. In any case, because the friction resistance between the metal of the sleeve and the glass top surface of the heater or ceramic top surface is large, the drive torque increases. If this state is continued, shaving of the inside of the metal sleeve advances and the drive torque further increases, and the metal sleeve serving as a fixing film may not be able to rotate or the metal sleeve may be broken. Moreover, the contact heat resistance between the heater and the metal sleeve is increased due to shaving powder and the heat efficiency may be deteriorated. Furthermore, it is necessary to secure the electrically insulating characteristic of the heater.
The present invention is made to solve the above problems and its object is to provide a heater having a preferable sliding characteristic against a rotator and an image heating apparatus using the heater.
It is another object of the present invention to provide a heater securing an insulating characteristic and an image heating apparatus using the heater.
It is further object of the present invention to provide an image heating apparatus comprising, a heater for heating an image on a recording material, which has a substrate and a heat generating resistor provided on the first plane of the substrate, a rotator which rotates while contacting with the second plane opposite to the first plane of the heater and has a metallic layer, wherein an imide-based slide layer is formed on the second plane of the heater.
It is further object of the present invention to provide a heater comprising, a substrate, a heat generating resistor, and a top-surface layer made of an imide-based resin provided on the plane opposite to the plane on which the heat generating resistor is provided.
It is still further object of the present invention to provide an image heating apparatus, comprising, a heater for heating an image on a recording material, which has a substrate and a heat-generating resistor provided for the substrate, a rotator rotating while contacting with the plane for which the heat generating resistor of the heater is provided and having a metallic layer, wherein an electrically insulating layer is formed on the heat generating resistor and an imide-based slide layer is formed on the electrically insulating layer.
It is still further object of the present invention to provide a heater comprising, a substrate, a heat generating resistor, an electrically insulating layer formed on the heat generating resistor, and a top-surface layer made of an imide-based resin formed on the electrically insulating layer.
Other objects of the present invention will become more apparent from the detailed description by referring to the accompanying drawings.